1. Field of the Invention
The present invention relates to a flexible multi-parameter cable having a plurality of different types of conductors for conducting signals relating to a plurality of different types of sensed parameters, and more particularly to a multi-conductor patient monitoring cable for conducting signals such as electrocardiogram, respiration, temperature and pulse oximetry signals, relating to a plurality of different types of sensed physiological conditions of a patient.
2. Description of the Prior Art
In hospitals and other health care environments, it is often necessary to continually collect and analyze a variety of different types of medical data from a patient. These data may include electrocardiogram (EKG) signals, body temperature, blood pressure, respiration, blood oxygen saturation, and other monitored physiological parameters.
Medical monitoring systems have typically fallen into one of two general categories: multi-parameter monitoring systems which collect, process and display all of the desired data; and small portable systems which monitor one or two of the various patient physiological parameters. Multi-parameter monitoring is typically provided at a higher care facility, such as an intensive care unit or hospital operating room, and generally results in a plurality of cables which extend between the patient and the monitor. For example, there may be anywhere from three to five cables for EKG, two for cardiac output, three for temperature, six for non-invasive pulse oximetry, etc. This array of cables interferes with the movement of personnel around the patient and furthermore presents an undesirable obstacle when the patient must be quickly transferred from one position to another, such as from his room bed to an operating room or an intensive care unit.
FIG. 1a illustrates a typical prior art arrangement wherein a patient 2 has a plurality of sensor leads, such as EKG leads 4, non-invasive pulse oximetry leads 6, temperature leads 8 and an air hose 10 for non-invasive blood pressure measurement, connected between the corresponding sensor apparatus on patient 2 and a respective one of monitor cables 12, 14, 16 and 18. Each of monitor cables 12-18 typically include a connector at one end which is received by a patient monitor 20 and a connector at its other end which receives the patient connected sensor leads 4-10.
One prior art attempt to provide management of the plurality of different types of leads and cables in a patient monitoring system is shown in, for example, Swiss Patent 524,992 and EPO 0 466 272. In these prior publications, it is indicated that a single junction box can receive each of the patient connected leads coupled to the individual patient sensors, and provide a common output cable from the junction box which is then connected to the patient monitor. Although the construction of the single output cable is not disclosed in these patents, it is expected that it merely comprises a bundling of the individual patient leads into a single jacketed structure, such as shown in FIG. 1b. Bundling is a conventional technique for cable management, as evidenced by U.S. Pat. No. 27,206. Although use of a single output cable improves cable management, there are serious electrical and mechanical problems associated with such a system. For example, the EKG sensors, being connected to the skin of the patient, are susceptible to picking-up very high voltage and/or high frequency signals when electrosurgery is being performed on the patient, or in the event that defibrillation becomes necessary. Under these circumstances the high voltage signals picked-up by the EKG leads may cause electromagnetic interference (EMI) which may be impressed upon the conductors carrying the other sensed patient signals, and thereby distort or otherwise corrupt these other signals. Furthermore, it is noted that when performing, for example, pulse oximetry sensing, it is required to provide relatively high current pulse signals to the oximetry sensor apparatus and a very low level and noise sensitive receive signal is required to be sensed and provided back to the monitor. Thus, when EKG cables are bundled in close proximity with pulse oximetry cables, the high level pulse currents on the pulse oximetry conductors can create electrical disturbances on the EKG signal conductors, and conversely, the high voltage signals on the EKG conductors can corrupt the data in the very sensitive pulse oximetry receive conductors. Still, furthermore, the EKG conductors can crosstalk among themselves, due to their being bundled together, and thereby degrade the common mode rejection of one pair of EKG conductors with respect to another pair. Even furthermore, the pick-up of high voltage defibrillation pulses by the EKG conductors can cause a breakdown of the voltage isolation between the closely spaced pins of the cable connector at the cable/monitor interface. Due to these electrical problems, a single cable which merely comprises a collection of the individual patient parameter cables bundled so as to be included in a single sheath, may be inadequate. Additionally, from a mechanical point of view, a cable as shown in FIG. 1b would be relatively heavy, thick, inflexible and bulky due to the plurality of individual shields and outer jackets included with each patient cable, as well as the requirement for a plurality of interstitial fillers which are added for improving the shape of the cable, but which unfortunately adds to its weight and inflexibility. Still further, due to the separated and non-symmetrically spaced arrangement of the cable bundles, each bundle, and each conductor in each bundle, must be constructed so as to have a maximum resistance to flexing failure. This necessarily increases the cost and complexity of the multi-parameter cable.
Another solution to the multi-parameter cable problem would be to provide active electrical signal processing inside of the junction box which would multiplex the multiple patient parameter signals onto a single output conductor or coaxial cable which is then received and demultiplexed by the monitor. Although this appears to be a satisfactory solution, it causes the junction box to become a much more expensive device, as well as undesirably increasing its size, introducing power requirements and decreasing its reliability. Additionally, since the junction box is positioned at the free end of the monitor cable, it is subject to being dropped on the floor, etc., when disconnected from the patient and therefore size, weight, flexibility and durability (as well as cost) are very important considerations.
Consequently, it is desirable to provide a multi-conductor cable which will provide continuity of the electrical signal handling properties of the leads connected to a plurality of different parameter sensors, when these leads are combined in a single multi-conductor cable, while at the same time prevent cross coupling of the signals. At the same time, it is desirable that this cable be flexible, light, of a small diameter, cost effective and relatively easy to construct.